Measurement of electrical resistivity of particulate entrained in a gas stream

Abstract

The resistivity of particulate matter in a gas stream, such as a combustion gas stream produced in a coal-fired power plant, is measured by collecting a sample of the particulate on the surface of a porous ceramic cylinder (62), either with or without an applied collection voltage, and then determining the resistance of the sample with a compound measurement electrode (82) having multiple conductors (84,86). The referece electrode (89) and the measurement electrode (82) are spirally wound on the ceramic cylinder (62) in an interdigitated manner, so that the two (82,98) are laterally adjacent down the length of the cylinder (62). The pressure within the cylinder (62) is controllable, with a pressure below atmospheric being applied to draw the particulate to the surface and ascertain when a sufficient sample for measurement is present, and a pressure above atmospheric being applied to blow away the sample after the measurement is completed, thereby preparing the instrument for the taking of another sample.

What is claimed is: 
     
       1. Particulate resistivity measurement apparatus, comprising: a substrate having a first side and a second side;   two adjacently positioned electrodes supported on the first side of the substrate, including a measurement electrode, and   a reference electrode;     means for applying a vacuum to the second side of the substrate to controllably draw gas through the substrate so that particulate matter carried by the gas is deposited on the first side of the substrate;   a measurement power supply that applies a measurement voltage between the reference electrode and the measurement electrode; and   a current measurement meter that measures the current flowing between the reference electrode and the measurement electrode due to the applied measurement voltage.   
     
     
       2. The apparatus of claim 1, wherein the substrate is cylindrical in shape. 
     
     
       3. The apparatus of claim 2, wherein the measurement electrode and the reference electrode are spirally wound in an interdigitated fashion on the substrate. 
     
     
       4. The apparatus of claim 1, further including a shield around the substrate. 
     
     
       5. The apparatus of claim 4, further including a collection power supply that applies a collection voltage between the shield, on the one hand, and the reference electrode and measurement electrode, on the other hand. 
     
     
       6. The apparatus of claim 1, further including means for applying a pressure to the second side of the substrate to controllably blow away particulate that has accumulated on the first side of the substrate.   
     
     
       7. The apparatus of claim 1, wherein the measurement electrode has a composite structure including a measurement conductor, a pair of confinement conductors, one on either side of the measurement conductor, and an insulation layer between each of the confinement conductors and the measurement conductor. 
     
     
       8. The apparatus of claim 7, wherein the confinement conductors and the measurement conductor are grounded. 
     
     
       9. Particulate resistivity measurement apparatus, comprising: a hollow cylindrical substrate made of an electrical insulator;   a pressure controller communicating with the interior of the substrate, the controller including a vacuum source and a pressurization source;   two interdigitated electrodes spirally wound on the substrate, including a measurement electrode, and   a reference electrode;     a measurement power supply that applies a measurement voltage between the measurement electrode and the reference electrode; and   a current measurement meter that measures the current flowing between the measurement electrode and the reference electrode due to the applied measurement voltage.   
     
     
       10. The apparatus of claim 9, wherein the measurement electrode is a compound electrode, including a measurement conductor, a pair of confinement conductors, on each side of the measurement conductor, and an insulation layer between each of the confinements conductors and the measurement conductor. 
     
     
       11. The apparatus of claim 10, wherein the pair of confinement conductors are grounded. 
     
     
       12. The apparatus of claim 9, further including a shield around the substrate. 
     
     
       13. The apparatus of claim 12, further including a collection power supply that applies a collection voltage between the shield, on the one hand, and the reference electrode and measurement electrode, on the other hand. 
     
     
       14. Particulate resistivity measurement apparatus, comprising: a cylindrical substrate that is sealed at the ends to permit control of the interior pressure of the substrate, and is made of a porous ceramic;   a pressure controller communicating with the interior of the substrate, the pressure controller including a vacuum source of a pressure below atmospheric,   a purging source of a pressure above atmospheric, and   a valve that is controllable to connect the interior of the substrate to either the vacuum source or the purging source;     a perforated shield around the exterior of the substrate;   two interdigitated electrodes spirally wound on the substrate, including a measurement electrode having a composite structure including a measurement conductor, a pair of confinement conductors, one at a greater cylindrical radius and one at a lesser cylindrical radius than the measurement conductor, and an insulation layer between each of the confinement conductors and the measurement conductor, each of the confinement conductors being at ground potential, and   a reference electrode;     a measurement power supply that applies a measurement voltage between the reference electrode and the measurement conductor of the measurement electrode; and   a current measurement meter that measures the current flowing between the reference electrode and the measurement conductor due to the applied measurement voltage.   
     
     
       15. The apparatus of claim 14, further including a shield around the substrate. 
     
     
       16. The apparatus of claim 15, further including a collection power supply that applies a collection voltage between the shield, on the one hand, and the reference electrode and measurement electrode, on the other hand.